Automatically variable resistance electrical device



Oct. 23, 1951 D. E. FRITZ 2,572,330

AUTOMATICALLY VARIABLE RESISTANCE ELECTRICAL DEVICE Filed April l1, 1950 DWAIN E. FRITZ ATTORNEY Patented Oct. 23, 1951 AUTDMATICALLY VARIABLE RESISTANCE ELECTRICAL DEVICE Dwain E. Fritz, Shaker Heights, Ohio, assignor to Jack & Heintz, Inc., Cleveland, Ohio, a corporation of Ohio Application April 11, 1950, Serial No. 155,308

(Cl. L-48) 3 Claims. l

This invention relatesl in general to electrical machines employing automatically variable resistance devices and more particularly to those machines employing relatively rotatable units, one of which carries a variable resistance device responsive to variations in speed of rotation of the rotatable unit.

It is common practice in variable resistance devices, such as in the Speed Responsive Rheestat shown in the U. S. Patent to Vacha, 2,460,246, January 25, 1949, to provide a stationary unit for carrying a carbon pile resistor, the compression of the stack of carbon discs of which is responsive to variations in speed of the centrifugally responsive rotary unit. This is made possible by means of actual continuous physical bearing contact between the rotary unit and the carbon pile stack to vary the compressive force applied to the car-bon pile stack.

Regardless of the construction of this physical bearing contact, friction and resulting wear is imminent which results in unevenly applied pressure and ultimately wear and eccentricity and uneven spacing of the resistance carbon pile discs and consequently malfunctioning of the variable resistance qualities of the assembly.

' One of the primary objects of my invention therefore is yto provide in such, and analogous devices, means whereby the resistance of the resistance device may be varied in response to variations in speed of rotation of the rotary unit by continuous pressure applied, without friction, by the rotary unit against the resistance device.

Another object is to provide means for applying the variable pressure to the resistance device without any physical contact between the rotary unit and the non-rotary unit or its resistance device.

A fur-ther object is to provide, instead of a physical bearing contact between the rotary unit and the resistance device, electrically opposed means, such as opposed magnets, carried by the rotary and stationary units, whereby, to the cornplete elimination of physical contact and friction,r

the resistance device is variably compressed in response to variations in speed of the rotary unit. With the foregoing and other objects in View, the invention resides in the combination of parts and in the details of construction hereinafter set forth in the following specification and appended claims, certain embodiments thereof being illustrated in the accompanying drawing which is a view partly in plan and partly in crosssection of a speed responsive rheostat, showing a centrifugal rotary unit and a non-rotary unit carrying a carbon pile resistor.

Referring more particularly to the drawing,

.gage the inside wall of the glass tube.

I have shown, for illustrative purposes, my invention as applied to a speed responsive rheostat comprising a rotary unit indicated generally at I0, connected with a rotating shaft I and a nonrotary unit generally indicated at l2 and mounted in a xed position in the stationary frame.

The rotating unit may include a stud I4 attached to the machine shaft I in any convenient manner. Secured to the stud I4 is a frame I8 with resilient side arms 20 arranged to receive the ends of a bowed at spring 22 to which are riveted the weights 24. A coil spring 26 bears between the base of the frame andthe middle of the spring 22. The spring is maintained in centered position surrounding a cylindrical boss 2'! on the base of the frame. Wing members 28 are attached -to the spring 22 by the same rivets which hold the weights 24. The center of the fia-t spring is provided with an opening to receive a retaining member 30.

The non-rotary unit I2 comprises a cup 32 on which are mounted two metal posts 34 carrying at the outer end a plate 36. Posts 34 and plate 36 are held in position by bolts 38, the plate being insulated from the bolts and posts by suitable insulating members indicated at 40. The entire assembly may be enclosed within a cover 4I A carbon pile 42, consisting of thin annular discs, is mounted lbetween the cup member 32 and the plate 3B. At its ends the pile engages floating contacts 43 and 44, to be later described in detail. An insulating supporting tube 45 for the pile, preferably of glass, passes through the holes in the discs and corresponding holes in the floating supports. The tube is held in place by members 46 and 48.

The member 46 comprises a small plug having inwardly extending spring iingers 50 to engage the inner walls of the tube. rlhe plug is received in a central opening in a central boss 53 formed on the plate 36. The peripheral portion of the plug bears against the oating support 44.

The member 48 at the inner end of the tube is similarly provided with spring iingers 54 to en- It will be noted that the fingers 50 and 54 are short enough so that they do not engage one another, and hence the tube forms an insulating support for the carbon pile. Suitably secured to member 48 is a permanent magnet 56, and suitably secured to retaining member 3Q is a permanent magnet 58. These magnets 56 and 58 are so disposed that their adjacent faces are of like polarity to oppose each other and of such strength as to be continuously spaced and out of frictional contact. 'The member 48 is grooved similarly to the plug 46 to receive the end of the glass tube. The peripheral portion of the member is adapted to engage the oating contact 43 under some circumstances to be presently described, for which purpose the member 48 is free to pass through a central hole in the cup'BZ'. It will be` appreciated that permanent magnet 56 or 58, or both, may be supplanted by a suitable electromagnet.

The construction of the floating contacts 43, and 44 will now be described. These are of special construction, in order, with the aid of opposed magnets 56 and 58, to apply true parallelpressure to all portions of the carbon discs. The contact 43 is a disc having arms 66 with feet 12 bolted under the posts 34. The entire member is preferably made from one integral piece. The Contact member 44 is of identical construction, but the feet 'l2 are engaged in electrical contact with the plate 36 and insulated from the posts 34. The springarins 68 act to urge the discs 43 and 44 to- Ward the cup 32 and plate 36, respectively.

The arms 66 and 68 are of spring material, and they may be adjusted with relation to their corresponding contact discs 43, 44 to urge the discs in one direction or the other. For the inner disc 43', the arrangement of the arms is such that the disc is urged into contact with the cup 32.v For the outer disc 44', the same setting may be used, in whichV case the arms tend to force the disc into engagement with the plate 36. Under these conditions the floating members themselves wouldv apply no compression t the pile. Or, as will be explained later, the outer disc 44 may be set with relation to the arms 66, so that the spring pressure of the arms forces the disc away from the plate 36; in other words, if no other forces were acting, the disc 44 would be spaced inwardly from the plate 36 to a slight extent. With such a setting the disc 44 is itself capable of applying some compressiveV force to the pile. The operation of the apparatus under both conditions will be described later.

The plug member 46 is urged to the left bya coil spring 14, the compression of which is adjusted by a screw plug 'I6 threaded into the boss 53. The speed for which the unit is to govern may be adjusted by varying the compression ofY the spring. An electrical lead 82 connects with the plate 36 which forms one terminal of the pile.

This lead may be connected with the shunt eld of the electrical machine in the usual manner. The other end of the pile is grounded to the frame by reason of the connection of member 43.

When the device is assembled the springs 22 and 26 of the rotating member are considerably compressed.k At standstill, the force due to these springs overcomes the force of the spring 14, so that the entire carbon pile unit is forced to the right, as shown in the drawing. The magnet retaining member 48 bears against the iioating member 43, and the member 44 is pressed against the plate 36. The carbon discs are under high leaves engagement therewith. At this time, the spring forces due to the rotating member and the spring 'I4 act only on the tube 45 and are ineffective to apply any compression, depending on the setting of the floating contact disc 44 in relation to its arms 66'. Arms 66 may beV adjusted in a manner to urge the disc 44 either toward or away from the plate 36. If the disc is urged toward plate 36, then at this time the pile will be under no compression and the resistance will be very high, practically infinite. The diminution of field current caused by the presence of this high resistance in the field circuit accelerates the speed-up of the machine. The space taken by the pile and floating members is slightly less than the space between the cup 32 and the plate 36, which constitute theV end supports for the pile, whereby a small lost motion is provided. The setting of the disc 44 to provide a substantially im'inite resistance is satisfactory in machines havinga light-series field, thus assuring rapid acceleration in theintermediate range.

For larger units, it may be necessary to maintain some shunt field current in order that the torque will not be too greatly reduced. To this end the disc 44 is set to be urged by its spring arms 66 away from the plate 36, that is, toward the pile, so that it applies some compression to the pile even when the other springs apply no compression thereto. The compression thus applied to the pile by the disc 44, in this intermediate range is less than that applied by the other springs of the unit in the starting or running range. The amount of compression, andV hence the maximum resistance in the intermediate range, may obviously be adjusted by the pressure applied by the floating disc 44.

In any case, as the speed further increases the force due to the rotating member further diminishes. UnderV the action of non-rotary spring 74 the plugV 46 then engages the oating disc 44 and the pile is again subjected to strong compression between the floating member 44 and the now non-rotary member 43. The control is now in the running range, wherein the discsare' variably compressed in dependence on speed. If the speed increases above the regulated value, the discs are compressed further to increaseV the eld current, and if speed is reduced, the compression isY relaxed to decrease the eld current, whereby the inverter speed is quickly restored to the desired value.

It will be seen that in the starting range the pile is compressed toward the right and in the l running range is compressed toward the left,

while the lost motion provides an intermediate condition of zero (or minimum). compression to accelerate the speeding up of the machine.V Between starting and running conditions, the pile compression so that the resistance is a minimum.`

Consequently, a high field current is available at starting.

As the machine is started, the forces due to rotation of the weights act in a manner to straighten the spring member 22, thus diminishing the opposing magnetic pressure of magnet 58 against the magnet 56. The magnet retaining member 48 moves toward the left under the urging of non-rotary spring 74. At some speed below the running range, the floating Contact member 43 bottoms against the cup 32 and the member 48 is shifted bodily from one position to the other. The spring forces of the rotary unit are made up of the forces due to the resilient arms 2E!Y of the frame, the flexure of the-fiat spring-22 and` the force due to the coil spring 26. The coil spring is desirable because the large force required for compression of the pile could not be provided by a flatspring of convenient size. The wing members 28 are used to flex the fiat spring 22 and compress the coil spring 26; they prevent any tendency of the flat spring to buckle.

The rotary unit is preferably so adjusted thatin the drawing. In this position the forces due tothe arms 20 and the flat spring 22 are relatively weak as compared with the corresponding forces under the starting condition when the spring 22 is bowed outwardly to a greater extent. Thus, in the running range, a soft and sensitive spring action is provided.

The arrangement of the opposed adjacent strong magnets 56 and 58 on the rotary and nonrotary units I0 and l2, respectively, precludes the possibility of surface engagement of the two magnets, whether they are both permanent magnets or one or both is an electromagnet. Their magnetic strength is predetermined for the true functioning of the assembly, taking into the strength of the springs of the rotary and nonrotary units and the speed responsive centrifugal Weights. This eliminates any possibility of friction between the rotary and non-rotary units and consequent wear and eccentricity of application of force by the rotary unit on the carbon pile. Such an eccentric application of force on the pile would result in eccentric wear on and misalignment of the carbon pile discs. This would result in uneven spacing between the discs and destroy the usefulness of the carbon pile.

I claim:

1. A centrifugal governor comprising a rotary unit provided with a centrifugal weight, a nonrotary pressure responsive resistance device including a carbon pile resistor, spaced magnetically opposed adjacent members carried by said rotary and non-rotary units, control means for controlling the linearly applied pressure on the resistance device by the rotary unit and for increasing the linearly applied pressure on the resistance device upon an increase of speed and for reducing the linearly applied pressure on a clecrease in speed without physical contact of said rotary unit with said non-rotary unit or its resistor.

2. A centrifugal governor comprising a rotary unit having a centrifugal weight, a non-rotary unit and a pressure responsive variable resistor carried thereby, spaced magnetically opposed adjacent members carried by said rotary and nonrotary units for preventing physical contact of said rotary unit with said non-rotary unit and resistor and for transmitting variable linearly applied pressure to said resistor in response to variations in speed of rotation of said rotary unit.

3. A centrifugal governor comprising a rotary unit having a centrifugal weight and spring means, a pressure responsive pile resistor, a nonrotary unit including end supports for said pile, a non-rotary spring and an axial supporting member for said pile, the non-rotary and rotary springs being disposed at opposite ends of said axial member, the pile being supported for bodily shifting between the end supports, means including spaced magnetically opposed adjacent members carried by said axial member and said rotary spring for applying linear pressure, without physical contact between said opposed members directly to the pile between the rotary unit and one end support under starting and running conditions, said springs being ineffective to act on the pile in an intermediate speed range during which the pile is bodily shifted between the supports.

DWAIN E. FRITZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Vacha Jan. 25, 1949 

